In recent years, with the growing of the technologies, lot types of electronic products are produced. The high-tech electronic devices are deeply combined with human's daily life. For example, each of the panels and the global positioning systems of automobiles, smart phones, tablet PCs, variety toys and remote-controlled apparatuses is part of the technology life of human nowadays. The mainly necessary elements in electronic devices are semiconductor elements, such like power semiconductors, transistors, amplifiers and switches, especially the power semiconductors are much more fabricated in industry.
For example, one of the common power semiconductors is an insulated gate bipolar transistor (hereinafter “IGBT”). The basic encapsulation of an IGBT is a power semiconductor with three terminals. The characteristics of IGBTs include high efficiency and high switching speed. Generally, IGBTs are developed to replace the bipolar junction transistors (or called BJTs). IGBTs have both the characteristics of field effect transistors (or called FET) and bipolar transistors, so the IGBTs can withstand high current load, the gate can be easily driven and the turn-on voltage drop is low. Under this circumstance, the common uses of IGBTs are applied to high-capacity power devices like switching power supplies, motor controllers and induction cookers.
On the other hand, even though IGBTs have been fabricated and used for tens of years, there are still some drawbacks of the process technology and semiconductor structure. Please refer to FIG. 1. FIG. 1 schematically illustrates the structure of a conventional insulated gate bipolar transistor of the prior art. A conventional trench punch-through IGBT includes a metal oxide semiconductor (or called MOS) layer 11, a N-type buffer layer 12 and a P-type injection layer 13. The MOS layer 11 is disposed between an emitter metal layer 111 and a N-type drift layer 112 for providing electron injection and controlling element switching. The N-type buffer layer 12 is used for conducting between the electrons and the electron holes and withstanding high voltage. For matching the specifications of product, a wafer backside thinning technology is used for reduce the resistance of the N-type drift layer 112, and a backside implant technology and a backside anneal technology are used for fabricating the N-type buffer layer 12 and the P-type injection layer 13 during the manufacturing process of the power semiconductor. The N-type buffer layer 12 is used for buffering the electric field and adjusting the concentration of the electron hole injection, and the P-type injection layer 13 is used for providing electron hole injection.
After the backside thinning process, the power semiconductor wafer becomes thinner so that the wafer is frangible and easy to bend. Meanwhile, since the metal process of the power semiconductor is done before the backside thinning process, the incoming anneal process is limited by the melting point of the surface metal, and the depth and the thickness of the N-type buffer layer and the P-type injection layer cannot be fabricated by the high-temperature drive-in process, in which the characteristics of power semiconductors and the process flexibility are limited everywhere.
There is a need of providing a manufacturing method of a power semiconductor to obviate the drawbacks encountered from the prior art.